urinary system

• The liver plays a tremendous role in directing dead cells and leftover chemicals to the digestive and urinary systems
• The liver can't actually escort waste out of your person
• The lungs can lend a hand, exhaling carbon dioxide, and the colon will eventually poop out unusable stuff and old cell-parts
• Much of your chemical waste still needs to be sorted and disposed of, so the urinary system steps in to bat clean-up
• Urinary system


  Regulates water volume, ion salt concentrations, pH levels, and influences red blood cell production and blood pressure
• Urinary system's main purpose

  Filters toxic leftovers from your blood and ferries it out of the body
• Most of what's in your blood is totally removed by the kidneys, then your body pulls back what it wants to hold onto, before the rest is sent to the bladder
• Metabolizing nutrients, especially protein


  Produces ammonia, which is toxic
• Liver


  Converts ammonia into less-toxic urea, which the kidneys filter out into pee
• Dirty, pee-soaked toilets and cat litter boxes smell like ammonia because urea can degrade back into ammonia
• Kidneys


  • Pair of dark red, fist-sized, bean-shaped organs that sit on each side of the spine against the posterior body wall
  • Retroperitoneal, meaning they lie between the dorsal wall and the peritoneum rather than inside the abdominal cavity
• Kidney layers


  • Outermost cortex
  • Medulla, a set of cone-shaped masses of tissue that secrete urine into tiny sac-like tubules
  • Innermost renal pelvis, a funnel-shaped tube surrounded by smooth muscle that uses peristalsis to move urine out of the kidney, into the ureter, and into the bladder
• Kidneys filter about 120 to 140 liters of blood every day
• Nephrons


  • Microscopic filtering units where blood-processing and pee-making begins
  • Consist of a renal corpuscle in the cortex and a long, winding renal tubule that loops between the cortex and medulla
• Nephron filtration, reabsorption, and secretion

  1. Filtration: Fluid, waste products, ions, glucose, and amino acids pass from blood into the glomerular capsule

  2. Reabsorption: Useful substances like ions, glucose, and water are reabsorbed back into the blood from the renal tubule

  3. Secretion: Remaining waste products are secreted into the tubule to be excreted as urine
• Renal tubule parts


  • Proximal convoluted tubule (PCT): Reabsorbs useful substances
  • Loop of Henle: Creates a salt concentration gradient to drive water reabsorption
  • Distal convoluted tubule (DCT): Urea is reabsorbed to maintain the salt gradient
• Urea is used by the kidneys to ramp up the concentration gradient in the medulla, making it more effective at drawing water out of the collecting duct
• Tubular secretion


  Selectively transports waste like hydrogen, potassium, and certain organic acids and bases from the blood into the urine
• The kidneys use filtration, reabsorption, and secretion to reabsorb water and nutrients back into the blood, and make urine with the leftovers